Have an 86 which I've owned for a couple of years. Recently decided to change oil (Mobil Synthetic), plugs (AC Delco) & wires (Accel 8.8). Car ran well before the change although the idle did run high and wander up and down a bit (rpm'd at 12 to 16). Thought that was a vaccum leak and began researching it in the archives. This became a down the road project on the task list as it didn't affect driving.

At the top of the project list now is what did I do wrong? It is running rough now at idle (rpm 8ish) and feels like it is missing when I am driving. I am getting some rear pipe feedback (snap, crackle and pop) when I come off the gas. I assume this is electrical and not fuel related?

The plugs I bought were an R43TS and I gapped them at .035. The book says to use a R43CTS. Is there a difference? Also followed the instructions on how to assemble the wires (had to add on the plug side head). Anybody have any thoughts on what it could be?

 

Is the Service Engine Soon light on? Could be many things but if there is a code it will narrow things down.

 

Put the old plug wires back on and see if problem goes away. If it does change out to the new wires one at a time. When you put one of the new ones on and the problem starts again there is your bad wire.

 

Use the process of elimination, and remember KISS
Keep
It
Simple
Stupid

 

KISS
Keep
It
Simple
Sir -- for when you are talking to the boss.

 

Is this a high mileage 86? If so then you don't want to be running Mobil 1 Synthetic in the vette. It will cause your problems. This only is only to be used in low mileage cars.

 

Maybe you cracked one of the new plugs when installing them? Maybe one that isn't easy to slip the socket over squarely, or racheting at an off angle? (#2 on my 85)

 

WRONG PLUGS!!!!! If you're using ACDelcos, with aluminum heads you should be using the 41-629s, you can verify this on the net going to ACDelcos site. We should periodoticaly check for vac. leaks when experiencing problems (a slow patience process), also the IAC could be suspect. And finally, are you sure you didn't cross a plug wire?...it's so damn easy to do!!

 

Good feedback everyone - thanks! I saved the wires (and old plugs) except for the #6 where I had to steal the 30 degree plug shroud from the old one (90 degree won't fit that plug). I will start with a wire replacement tomorrow.

Should have mentioned that it's an iron head and not aluminum (I understand most 86's are iron). Also, what's high mileage? I'm in the low 70's (first time around). Please tell me both those problems are gone with this explanation.

 

Oh and I was very careful not to cross a plug wire but I will re-check the schematic tomorrow. What's the IAC? And although I've looked for it, I have never found a schematic for checking for vacuum leaks. I believe I have heard it is posted inside the engine compartment somewhere but I haven't been able to find it.

 

We've all been there before, before you start replacing plug wires..ohm them, using a digital voltage ohm meter they should read about 5000 ohms per foot, try to twist them while doing the ohms test..to see if there is a bad or broken connection in between!! STILL, go to the ACDelco site to check on #s..... should have asked about Iron vs. Aluminum, my bad.

No, the IAC (idle air control) is located at the front of the engine..located below the TB.

 

LLOONNGG Day. Began early this NJ morn. Let's review what I know. Car running good. Change old wires and plugs. Car running bad, sounds electrical like its missing. Won't idle long, stalls after wandering from 10 rpm down and when I get on it it misses a bit, then backfires coming off the rpm. So I am almost certain it's electrical.

So we KISS it. Look for old wires to begin exchanging one at a time to see if I can find the offending item. WIFE THREW THEM OUT DURING THE WEEK. Have a melt down. Re-establish rules regarding touching my stuff. BUT, she bought it for me for our 20th so what can I say? I wisely choose to shut up.

Pull every wire one at a time. Check they aren't crossed and they are in the correct order which I believe to be (hope this comes out):

Left side Right side
Cylinders Distr Cylinders
8 l 6-5 l 7
6 l 3---7 l 5
4 l 4---2 l 3
2 l 8-1 l 1

Looking From the Front of car

Everything is fine there. Pull every wire and every plug individually and look. While I have the wires off I resize them because I had them too long. Pull the boot, cut the wire, reset the boot. Make sure every plug is properly screwed in. Make sure every boot is on tight at plug and distributer. Never opened the distributer so shouldn't be that.

Take car out for run. It is running worse! Come back, recheck every connection. Take car out - still awful. Car idles up and down for 30 seconds before quiting. Wound every wire from the distributer to the plug around one another at the suggestion of a friend (touching each other) instead of cleanly separated using separators. Still runs bad.

I'm sure it has to be something simple. Something I did. Could it be the Accel wires? Seating those boots is a pain. I followed the instructions but I don't know. At this point I'm not sure what to do next. Would sure love to drive it!

Rick - to respond to your quote above: How do I check the IAC, I checked on the ACDelco site for R43TS vs R43CTS but no info, never used an OHM meter (I'm a novice) but a friend has one and I'll test the wires.

What is my next step?

 

It ran good before, you changed wires and plugs and oil, nothing else. Let's rule out oil. That leaves what? I am not in the least familiar with cutting and putting ends on spark plug wires, but my sometimes faulty logic keeps coming back to the wires. Anyone else?

 

I'm trying to understand your distributor numbers in red. Firing order you've got is 1-8-4-3-6-5-7-2, right? Also, the wrapping wires is a new one to me..I'd been told that you don't want your wires to cross; the fewer overlaps the better.

 

Thanks for the feedback guys. This is driving me crazy. Weather's too nice not to be driving it and I lost the WHOLE summer last year because my 4+3 lost Reverse 1st and 2nd (that was a $3,500 reconfiguration of my budget which I finally did last fall after re-mortgaging the HOUSE)!
I am pretty certain my problem has something to do with the replacements I did and I am sure you are right to rule out oil. I'm sure this is electric which means wires or plugs are probably to blame.
Regarding the firing order - I currently have the cylinder order (looking at the distributer from the top and going clockwise starting in the 12:30position) 5-7-2-1-8-4-3-6! According to information I have and how I pulled them off that is right - right?
The wrapping the wires suggestion came from an early C3 guy. I have a sneaky suspicion that crossing wires may have been advantagous back then but I'm thinking that may not be true any longer. Anyone have a strong feeling on the subject?
Back to the car. I paid $85 bucks for the Accel wires thinking that I would upgrade to the 8.8mm size now in case I add performance mods later (re-mortgaging it two years. I didn't know they came un-booted from the factory. I was very careful booting them. I guess it's possible I screwed that up. Do I take them off and throw them into storage and go out and buy ACDelco originals (8mm's)? And does anyone know a good site to check whether ACDelco R43TS is the same as a R43CTS plug? I did some checking and they pull the same plug when cross referenced with another brand of plug.

 

I just changed plugs in my Vette today and it would barely run. After some trouble shooting, I found that I had 2 plugs that were bad. Although they were new, they were still bad.

I replaced them with 2 old plugs and everything cleared up and it runs fine. Tomorrow I will go out and replace with new plugs.

 

Dave: I think you cracked a plug, mixed up 5+7, or had a problem putting the wires together.

Pull the plugs + inspect carefully, ohm them from the cap to the center electrode. (if one is broken it will be open)

Ohm the wires as previously suggested. (you did put the center wire under the crimp end when assembling the plug wires) <sorry>

Don't change the oil (M1 is fine) or check other stuff. (if it did run ok before).


PS: Un-twist your wires. Run them neatly using stock routing.

 

Just got back - ready for the next stage. OK - Untwisting the wires is the easy part. I guess I may have cracked a plug so I'll take your suggestion and Ohm them and the wires (being unfamilar with this process I will learn). Also, will double check 5 & 7 for cross attachment.

I did put the center wire under the crimp and used a hammer and the two setting tools they provide to attach the crimp onto the wire. None of the center wires stick out passed the end of the crimp although the center wires seem to have a covering of some kind over them and the directions say not to cut or fray that covering.

I'll let you know what the outcome is. Again - thanks!

 

Neighbor with the Ohm meter isn't home (OK - so I'll buy one) so instead I reset the drivers side door panel (which I had to do a ton of rivet, glue and screw repair work on when I replaced the inner and outer seals) and did a general engine cleaning. Looks like I won't get a chance to test out your excellent suggestions until next weekend.
Everyone have a great week!

 

Rick - following up on our thread from last week. I got an Ohm meter. I read the information on the Accel box and it tells me that this 8.8 mm wire has 500 ohms of resistance per foot of wire. I have a wire that is approximately 28 inches long (#7).
I placed the red probe in the red end of the spark plug wire and the same with the black probe/wire. I turned on the meter and it is bouncing all over the place. Usually from 0 to .250 on the meter. It seems to bounce into the .200 range more often than other numbers.
My question is - what does this mean?